1. Field of the Invention
The present invention relates to cushioning material for forming press used for pressing of decorative laminates, printed circuit boards, copper-clad laminates (CCL), flexible printed circuit material (FPC), electrical laminates and so on.
2. Description of the Background Art
Referring to FIG. 1, when a laminate is to be manufactured by hot press, generally, an object to be pressed is interposed between heating platens 1 and 2, and a prescribed pressure and heat are applied thereto. At this time of pressing, as shown in the figure, metal mirror plates 4 and 5 are arranged at positions directly in contact with the object 3 to be pressed. Further, in order to apply uniform pressure and heat to the entire surface of the object to be pressed, a flat cushioning material 6 is positioned between heating platen 1 and metal mirror plate 4, and a flat cushioning material 7 is positioned between heating platen 2 and metal mirror plate 5.
A primary object of interposing cushioning materials 6 and 7 is to obtain a laminate having superior thickness precision and superior surface smoothness, by applying uniform pressure and uniform heat to the entire surface of the object 3 to be pressed. Therefore, cushioning property, thermal conductivity, heat resistance, durability, dimensional stability, surface releasing property and so on are necessary requirements of cushioning materials 6 and 7.
Several sheets, for example about 5 to about 20 sheets of kraft paper superimposed on one another have been long used as the cushioning material for forming press. The cushioning material consisting of kraft paper is inexpensive, and it exhibits superior cushioning property at the initial stage of use. However, durability for repetitive use is rather poor, and its working life is only one to at most 5 times of use. Because of such disadvantage, cushioning material formed of kraft paper has gone out of use recently.
Cushioning materials having various structures have been proposed as having improved durability.
One example includes a reinforcing woven fabric embedded in a rubber sheet 8, such as shown in FIG. 2. This cushioning material is superior to the one formed of kraft paper in its durability for repetitive use. However, since there is not a space in rubber, when it receives compressive force, side portions which are open expand, causing elongation or permanent set. This change in dimension affects the quality of the laminate to be pressed. In order to suppress such change in dimension, reinforcing woven fabric 9 is embedded. However, by the provision of reinforcing woven fabric 9, rubber elasticity is lost, and as a result, advantages of rubber sheet 8 such as good cushioning property and the effect of making uniform the pressure are lost. Further, since it does not have any space, thermal conductivity is so good that variation in temperature of heating platens is directly transmitted, causing variation in thermal conductivity.
FIG. 3 shows a cushioning material prepared by needle punching non-woven fabric layer 10 with reinforcing foundation fabrics 11 interposed therebetween. Reinforcing foundation fabric 11 embedded in non-woven fabric layer 10 may be one layer or two or more layers. This cushioning material has good cushioning property as non-woven fabric layer 10 includes spaces, and it also has good heat insulating effect. As for compressive force, unlike rubber, expansion in the direction of the side surfaces does not occur. In other words, dimensional stability with respect to compression is satisfactory.
Though the cushioning material formed of the needle punched non-woven fabric such as shown in FIG. 3 has the above described advantages, it suffers from the following disadvantages. A non-woven fabric essentially includes ups and downs at its surface and has uneven area weight. Such ups and downs at the surface and the uneven area weight causes variation in thermal conductivity and variation in pressure. In addition, needle punching leads to further unevenness in area weight. The ratio of spaces in the non-woven fabric decreases with long time of use, and therefore thermal conductivity and cushioning property change with time. By contrast, rubber layer 8 shown in FIG. 2 experiences less change with time, since it does not have any space.
A cushioning material shown in FIG. 4 includes rubber layers 13 with a reinforcing woven fabric 12 interposed therebetween, and needle punched non-woven fabric layers 14 and 15 such as shown in FIG. 3 on upper and lower surfaces of the rubber layers 13. The cushioning material has superior cushioning property of non-woven fabric layers 14 and 15 as well as superior stability with time of rubber layer 13. However, since non-woven fabric layers 14 and 15 are on the outermost surfaces, disadvantages of the non-woven fabric layer, that is, ups and downs of the surface and uneven area weight are directly reflected on the cushioning material.
A cushioning material shown in FIG. 5 is prepared by superimposing needle punched non-woven fabric layers 16 and 17 with an adhesive material 18, which is a glass cloth impregnated with epoxy resin, interposed. Since multiple layers of non-woven fabrics are superimposed in this manner, uneven area weight of each non-woven fabric layer can be offset to some extent. However, since non-woven fabric layers 16 and 17 still exist on the outermost surfaces, the aforementioned disadvantage inherent to the non-woven fabric layer cannot be thoroughly eliminated. Further, the adhesive material described above is hard, and therefore it cannot follow at all the change in shape of non-woven fabric layers 16 and 17 when compressive force is applied. Hence there is a possible problem of separation of the adhesive material caused by damage of glass cloth when the cushioning material is used for a long period of time.
A cushioning material 19 shown in FIG. 6 is a paper-like material prepared by mixing aromatic polyamide fiber and rock wool. The cushioning material has superior heat resistance, experiences small change in dimension thanks to its material, and it also has the advantage of smaller variation of area weight. However, it has the following disadvantages. Namely, it has poor cushioning property, it has small ups and downs on its surface as it includes fiber material, and layers tend to separate from each other.
FIG. 7 shows a cushioning material for forming press disclosed in Japanese Patent Publication No. 47-46945. The cushioning material has rubber layers 21 and 22 on an upper surface and a lower surface of a needle punched non-woven fabric layer 20. It is described that silicone rubber, nitrile rubber, butyl rubber or the like may be used for the rubber layer. FIG. 8 is an enlargement of the cross section of FIG. 7.
The cushioning material shown in FIG. 7 has superior cushioning property of the needle punched non-woven fabric, as well as the effect of making uniform the pressure because of rubber elasticity of the surface rubber layers. Different from the cushioning materials shown in FIGS. 3 to 5, the cushioning material has rubber layers 21 and 22 positioned on the upper and lower surfaces of needle punched non-woven fabric layer 20. Therefore, it is superior in that undesirable influences of ups and downs of the surface and uneven area weight of the needle punched non-woven fabric can be offset by the rubber layers 21 and 22. This is because the unevenness of area weight and ups and downs of the surface can be absorbed by fluidized rubber entering irregular spaces of the fibers at the surface of non-woven fabric layer at the interface between non-woven fabric layer 20 and rubber layers 21 and 22 as shown in FIG. 8, when rubber layers 21 and 22 are vulcanized and bonded to non-woven fabric layer 20 during the steps of manufacturing the cushioning material.
However, the cushioning material for forming press disclosed in Japanese Patent Publication No. 47-46945 has the following disadvantages.
First, since there is not a reinforcing material interposed in needle punched non-woven fabric layer 20 at all, needle punched non-woven fabric layer 20 moves following the change in shape of rubber layers 21 and 22 when the cushioning material is used, resulting in uneven pressure.
Secondly, rubber layers 21 and 22 are not sufficient to remove the undesired influence of uneven area weight of the non-woven fabric layer.
Third problem is the undesired influence caused by exudation of compounding agent contained in rubber layers 21 and 22. While the cushioning material is used under heat and pressure, compounding agent having low molecular weight exudes to the surfaces of rubber layers 21 and 22. When the exudation is left as it is, appearance of the cushioning material for forming press would be damaged, and in addition, there is a possibility that the exudation stains the mirror plate or the laminate to be pressed, or that the cushioning material is adhered to the mirror plate or the heating platen. In order to prevent exudation of the compounding agent, an exudation preventing layer such as a film or a metal foil may be adhered on the surfaces of rubber layers 21 and 22. However, actually, this approach has been not very successful, since an adhesive agent which is set causes uneven distribution of pressure, resulting in uneven pressurization, and poor heat resistance of the adhesive agent leads to the problem of uneven thermal conductivity or the problem of separation.
An object of the present invention is to provide a cushioning material for forming press which allows transmission of uniform pressure to the entire surface for a long period of time.
Another object of the present invention is to provide a cushioning material for forming press which exhibits uniform thermal conductivity over the entire surface.
A still further object of the present invention is to provide a cushioning material for forming press having superior dimensional stability.
A still further object of the present invention is to provide a cushioning material for forming press which neither stains a mirror plate or a laminate to be pressed, nor adheres to the mirror plate or a heating platen.
The cushioning material for forming press in accordance with the present invention includes two or more fiber material layers, a bonding material layer positioned between each of the fiber material layers for bonding upper and lower fiber material layers, an upper rubber layer positioned on an upper surface of an uppermost fiber material layer, and a lower rubber layer positioned on a lower surface of a lowermost fiber material layer.
Porous fiber material having spaces therein is preferred as the fiber material layer. Since such porous fiber material layer has spaces therein, it exhibits superior cushioning property. Non-woven fabric, woven fabric or paper may be employed as such fiber material layer.
Since rubber layers are provided on the upper surface of the uppermost fiber material layer and on the lower surface of the lowermost fiber material layer, when the rubber layers are superimposed on the fiber material layers and vulcanized and bonded during the steps of manufacturing the cushioning material, the fluidized rubber enters irregular spaces of the fiber on the surface of the fiber material layers at the interface between the fiber material layers and the rubber layers. As a result, uneven area weight and ups and downs of the surface of the fiber material layers are absorbed by the rubber layer. Accordingly, undesirable influence caused by unevenness of the fiber can be prevented, and uniform pressure distribution and uniform thermal conductivity can be obtained.
Preferably, the cushioning material for forming press in accordance with the present invention includes, for the purpose of improving releasing property, an upper releasing layer positioned on the upper surface of the upper rubber layer and a lower releasing layer positioned on the lower surface of the lower rubber layer. A synthetic resin film, a metal foil, a woven fabric, paper or the like may be used as the releasing layer.
More preferably, the upper releasing layer serves as an upper exudation preventing layer for preventing exudation of the compounding agent included in the upper rubber layer, and the lower releasing layer serves as a lower exudation preventing layer for preventing exudation of the compounding agent included in the lower rubber layer. In this case, since the exudation preventing layers are provided on the surfaces of rubber layers, the compounding agent having low molecular weight included in rubber never exudes. Therefore, stain can be prevented and releasing property can be improved.
The exudation preventing layer is preferably formed of a film-like material having both impermeability to air and releasing property. Such a material specifically includes a synthetic resin film, a metal foil and the like. Though a woven fabric and paper have air permeability, these may be used as exudation preventing layer when they are treated to have impermeability to air, for example by coating a synthetic resin liquid, laminating a synthetic resin film or by heat treating surfaces of these. When the woven fabric or paper is to be used as the exudation preventing layer by providing coating of synthetic resin liquid, polyimide resin, fluoride resin, melamine resin, acrylic resin or the like may be used as the synthetic resin liquid.
All the fiber material layers may be formed of the same material, or they may differ. When all the fiber material layers are of the same material, coefficient of thermal expansion of all the fiber material layers is the same, therefore warp is not generated in the cushioning material, and uniform pressure distribution and uniform thermal conductivity can be easily obtained. Further, manufacturing is easy.
If fiber material layers are formed of different materials, advantages of respective materials can be synergistically obtained, while disadvantages of respective materials can be offset. However, different materials of fiber material layers have different coefficients of thermal expansion, and therefore in order to prevent warp of the cushioning material, combination of the materials in the upper portion and the lower portion should preferably by symmetrical.
In one embodiment, the bonding material layer has an adhesive agent. A heat resistant rubber or synthetic resin adhesive agent may be used, or alternatively, a liquid type or sheet type adhesive agent may be used. Preferable example includes fluoroelastomer adhesive agent, silicone rubber adhesive agent, hydrogenated nitrile rubber adhesive agent, EPM adhesive agent, EPDM adhesive agent, acrylic rubber adhesive agent, NBR adhesive agent, epoxy resin adhesive agent, polyimide resin adhesive agent and so on.
In the present invention, two or more fiber material layers are laminated to obtain multilayered structure with a bonding material layer interposed. Therefore, uneven area weight of each fiber material layer can be offset, and precision of area weight of the cushioning material as a whole can be improved. Therefore, uniform pressure distribution and uniform thermal conductivity can be obtained. The larger the number of fiber material layers to be laminated, the higher the precision of area weight.
In one embodiment, the bonding material layer has a sheet-like base material which suffers from small amount of deformation in the planar direction when subjected to heat or pressure, and an adhesive agent applied on opposing surfaces of the base material. An woven fabric, a synthetic resin film, a metal foil, inorganic fiber paper may be used as the base material. As the adhesive, heat resistant rubber or synthetic resin adhesive agent may be used. More specifically, fluoroelastomer adhesive agent, silicone rubber adhesive agent, hydrogenated nitrile rubber adhesive agent, EPM adhesive agent, EPDM adhesive agent, acrylic rubber adhesive agent, NBR adhesive agent, epoxy resin adhesive agent, polyimide resin adhesive agent or the like may be used. Fluoroelastomer adhesive agent, EPDM adhesive agent or polyimide resin adhesive agent is preferable.
In this embodiment also, two or more fiber material layers are laminated to obtain multilayered structure with a bonding material layer interposed, so that unevenness area weight of each fiber material layer can be offset and precision of area weight of the cushioning material as a whole can be improved. As a result, uniform pressure distribution and uniform thermal conductivity can be obtained. As the cushioning material is used repetitively and repeatedly subjected to heat and pressure, the rubber layer tends to expand in the planar direction. However, as the bonding material layer suppressing movement of the fiber material layer in the planar direction is placed between the fiber materials, movement of the fiber material layers following the expansion of the rubber layer can be prevented. Therefore, dimensional variation can be suppressed even when the material is used for a long period of time, and uniform distribution of pressure is maintained.
In one embodiment, the bonding material layer is a rubber sheet. In this case, the rubber sheet may be one in which reinforcing woven fabric is embedded.
In one embodiment, the fiber material layer is a non-woven fabric, the bonding material layer is a foundation fabric, and the non-woven fabric and the foundation fabric are bonded by tangling between the fibers and the foundation fabric caused by needle punching. When the cushioning material is used repeatedly and subjected to repeated heat and pressure, the rubber layer tends to expand in the planar direction. However, since the fiber material layer is reinforced by the foundation fabric, movement of the fiber material layer following the expansion of the rubber layer can be prevented. Therefore, dimensional variation can be suppressed even if the cushioning material is used for a long period of time, and uniform distribution of pressure can be maintained.
In this embodiment, an adhesive agent may be applied to the foundation fabric so that the non-woven fabric and the foundation fabric are bonded not only by the tangling between fibers and foundation fabric caused by needle punching but also by adhesion by the adhesive agent. This results in firm bonding and further improvement of dimensional stability.
In one embodiment, the fiber material layer is a non-woven fabric and a first bonding material layer is a foundation fabric. The non-woven fabric and the foundation fabric are bonded by tangling between the fibers and the foundation fabric caused by needle punching. A second bonding material layer has an adhesive agent. As for the lamination of the fiber material layer and the bonding material layer, multiple stages of bonded non-woven fabric layers prepared by bonding two or more non-woven fabric layers by means of the first bonding material layer are laminated by means of the second bonding material layer. According to this embodiment, since the bonded non-woven fabric layer is reinforced by the foundation fabric, it has good dimensional stability. Since the bonded non-woven fabric layers are laminated in multiple stages by means of the second bonding material layer, unevenness of area weight of the bonded non-woven fabric layers can be offset, precision of area weight of the cushioning material as a whole can be improved, and hence uniform pressure distribution and uniform thermal conductivity can be obtained. The larger the number of lamination, the better the precision of area weight. As in the above described embodiments, heat resistant rubber adhesive agent or synthetic resin adhesive agent may be used as the adhesive agent.
In the above described embodiment, the second bonding material layer has a sheet-like base material which suffers from small amount of deformation in planar direction when subjected to heat or pressure, and an adhesive agent applied on opposing surfaces of the base material. This contribute to further improvement of the dimensional stability of the cushioning material as a whole.
In the above embodiment, an adhesive agent is applied to the foundation fabric of the first bonding material layer, for example. The non-woven fabric and the foundation fabric are bonded by tangling between the fibers and the foundation fabric caused by needle punching as well as by adhesion by adhesive agent. This further improves dimensional stability of the bonded non-woven fabric layer, and hence dimensional stability of the cushioning material as a whole can be improved.
When the bonding material layer has an adhesive agent, preferably, a fluoroelastomer adhesive agent is used. Fluoroelastomer adhesive agent has superior heat resistance. Further, since it is rubber adhesive agent, it exhibits superior flexibility even after vulcanization and bonding, not deteriorating cushioning property of the fiber material layer.
Generally, polyamide fiber, polyester fiber, melamine fiber, polyphenylene sulfide fiber or the like is used for the fiber material layer. Preferably, a heat resistance fiber, of which glass transition temperature is at least 200xc2x0 C. and the temperature at which weight loss of 10% is caused by thermal decomposition is at least 400xc2x0 C., is used. Such heat resistant fiber may be heat resistant organic fiber or inorganic fiber. The heat resistant organic fiber includes aromatic polyimide fiber, polyamide fiber, aromatic polyester fiber and so on. The inorganic fiber includes glass fiber, rock wool fiber, silica fiber, metal fiber and the like. One of these heat resistant fibers or two or more of these mixed are used in the form of non-woven fabric, woven fabric or paper.
In a preferred embodiment, an acrylic monomer is added in the composition forming the upper and lower rubber layers. Addition of acrylic monomer allows direct adhesion between the rubber layer and the releasing layer, without inserting an adhesive agent layer. Therefore, the manufacturing process can be simplified.
In a preferred embodiment, the upper rubber layer and the upper releasing layer are adhered without any adhesive agent, and the lower rubber layer and the lower releasing layer are adhered without any adhesive agent. As the rubber layer and the releasing layer are adhered without adhesive agent, unevenness of pressure and of thermal conductivity caused by the adhesive agent can be prevented.
Preferably, the temperature at which weight loss of 10% is caused by thermal decomposition of upper and lower rubber layers is at least 380xc2x0 C. A heat resistant rubber may be used as a material of the rubber layer. More specifically, fluoroelastomer, EPM, EPDM, hydrogenated nitrile rubber, silicone rubber, acrylic rubber, butyl rubber are preferable. These rubber materials may be used by itself, or blended or mixed with other organic or inorganic material. The compounding agent and the compounding ratio of the rubber layer mainly formed of the rubber material should preferably be adjusted so that the temperature at which the weight loss of 10% is caused by thermal decomposition is at least 380xc2x0 C.
Preferably, the primary component of the upper and lower rubber layers is a highly heat resistant fluoroelastomer.
More preferably, the upper and lower releasing layers are formed by a fluoride resin film serving as the exudation preventing layer. The property required of the exudation preventing layer is that exudation of the compounding agent in the rubber can be effectively prevented. Further, a material having modulus of elasticity close to that of rubber is preferable. If such requirements are satisfied, the elasticity of the rubber layer can be effectively utilized on the surfaces of the cushioning material, so that unevenness of pressure caused by ups and downs of the surfaces of the heating platen and the mirror plate can be absorbed by the rubber layer, and thermal expansion or contraction of the heating platen and the mirror plate can be followed. Thus uniform pressure distribution and uniform thermal conductivity can be obtained.
In view of the foregoing, the exudation preventing layer should preferably be formed by a fluoride resin film. Among fluoride resin films, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are particularly preferable. When a fluoride resin film is used as the exudation preventing layer, it is effective if it has the thickness in the range of from 10 xcexcm to 200 xcexcm. Preferable range of thickness is from 50 xcexcm to 100 xcexcm.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.